The ink jet recording apparatus is an image forming apparatus for printing by jetting out (spray) ink on a sheet functioning as a recording sheet. The ink jet recording apparatus is generally provided with an ink cartridge including an ink tank. The ink is supplied from the ink cartridge to a print head. Then, the ink is jetted out from the print head onto the sheet.
In using such ink jet recording apparatus, it is necessary to replace the ink cartridge when the ink in the ink cartridge runs out (depletes). Thus, it is necessary to detect (measure) and inform how much ink is left in the ink cartridge (ink remaining amount).
In view of this, various ink cartridges have been suggested, in which the ink remaining amount can be detected. For example, Japanese Publication of Unexamined Patent Application, Tokukaihei, No. 3-288654 (published on Dec. 18, 1991) discloses an ink cartridge provided with an ink absorbing foam material in an ink tank, a filter in an ink supplying path that connects the ink tank and a print head, and electrodes in a downstream of the filter, that is, at a location between the filter and an ink jetting outlet, the electrodes detecting whether the ink is present or absent in the ink supplying path.
In an ink jet recording apparatus using such an ink cartridge, the ink is supplied from the ink cartridge to the print head by a negative pressure applied via the filter from a print head side, which is an ink spraying outlet side.
The ink jet recording apparatus using such ink cartridge is so arranged that detection of the ink in the ink supplying path is carried out by using a current flowing between the electrodes. That is, the ink becomes absent in the ink supplying path when an ink remaining amount becomes little, thereby allowing no current to flow between the electrodes. It is detected that no current flows between the electrode. Thereby, it is judged as “ink empty (ink depletion)”, that is, it is judged that the ink has run out.
However, in applying the negative pressure via a filter from the print head side (the ink spraying outlet side) in order to suck out the ink, there is a possibility that printing quality would be deteriorated if the air is sucked in from the print head side.
In order to solve this problem, various methods to prevent the air from being entrained into the ink from the print head have been suggested. For example, in Japanese Publication of Unexamined Patent Application, Tokukai, No. 2002-36557 (published on Feb. 5, 2002), a buoyant force applied on an air bubble in an ink supplying chamber is set to be larger than a drag force given by velocity of flow of ink, thereby preventing the air bubble from growing in the ink supplying chamber.
Moreover, Japanese Publication of Unexamined Patent Application, Tokukai, No. 2002-67353 (published on Mar. 5, 2002) discloses an arrangement in which a first filter for preventing ink leakage and a second filter, which is finer than the first filter, for removing foreign materials are provided in an ink supplying path in this order from an upstream of the ink supplying path.
However, a larger air bubble is easy to break. Thus, in the art described in Japanese Publication of Unexamined Patent Application, Tokukai, No. 2002-36557, there is a possibility that an survived air bubble, which has not broken, enters the ink supplying chamber.
Further, in the art described in Japanese Publication of Unexamined Patent Application, Tokukai, No. 2002-36557, there is a problem that the air bubble gives influence on detection of ink depletion.
Moreover, in Japanese Publication of Unexamined Patent Application, Tokukai, No. 2002-67353, there is a problem that the second filter, which is finer than the first filter, produces a smaller air bubble, thereby deteriorating accuracy in detection of the ink depletion.